U.S. patent application number 10/587564 was filed with the patent office on 2008-02-14 for process for the treatment of fibre material and new composition.
Invention is credited to Jonni Ahlgren, Jukka Jakara, Seung-Hoon Lee, Aarto Paren, Jukka Rautiainen.
Application Number | 20080035287 10/587564 |
Document ID | / |
Family ID | 31725769 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080035287 |
Kind Code |
A1 |
Lee; Seung-Hoon ; et
al. |
February 14, 2008 |
Process For The Treatment Of Fibre Material And New Composition
Abstract
The invention relates to a process for the treatment of a fibre
material comprising the step of contacting the fibre material in an
aqueous medium with a chelating agent and a polymer having
following general formula ##STR1## wherein R.sub.1 is a hydrogen
atom or an alkyl group containing 1 to 12 carbon atoms, R.sub.2 is
--COOM or --CH.sub.2COOM, M is a hydrogen atom, an alkali metal
ion, an alkaline earth metal ion, an ammonium ion or a mixture
thereof, n, m and k are molar ratios of corresponding monomers,
wherein n is 0 to 0.95, m is 0.05 to 0.9, and k is 0 to 0.8, and
(n+m+k) equals 1, and the weight average molecular weight is
between 500 and 20,000,000 g/mol. The invention also relates to a
composition comprising a chelating agent and the above polymer.
Inventors: |
Lee; Seung-Hoon;
(Kyunggi-do, KR) ; Ahlgren; Jonni; (Vaasa, FI)
; Jakara; Jukka; (Siivikkala, FI) ; Paren;
Aarto; (Vaasa, FI) ; Rautiainen; Jukka;
(Espoo, FI) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
31725769 |
Appl. No.: |
10/587564 |
Filed: |
February 23, 2005 |
PCT Filed: |
February 23, 2005 |
PCT NO: |
PCT/FI05/00113 |
371 Date: |
June 13, 2007 |
Current U.S.
Class: |
162/72 ;
524/252 |
Current CPC
Class: |
Y02W 30/648 20150501;
D21C 9/163 20130101; D06L 4/12 20170101; D21C 5/02 20130101; D06P
5/132 20130101; D21C 9/1042 20130101; Y02W 30/64 20150501 |
Class at
Publication: |
162/072 ;
524/252 |
International
Class: |
D21C 9/10 20060101
D21C009/10; D21C 9/16 20060101 D21C009/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2004 |
FI |
20040293 |
Claims
1. A process for the treatment of a fibre material comprising
contacting the fibre material in an aqueous medium with a chelating
agent and a polymer having the following general formula ##STR13##
wherein R.sub.1 is a hydrogen atom or an alkyl group containing 1
to 12 carbon atoms, R.sub.2 is --COOM or --CH.sub.2COOM, M is a
hydrogen atom, an alkali metal ion, an alkaline earth metal ion, an
ammonium ion or a mixture thereof, n, m and k are molar ratios of
corresponding monomers, wherein n is 0 to 0.95, m is 0.05 to 0.9,
and k is 0 to 0.8, and (n+m+k) equals 1, and the weight average
molecular weight is between 500 and 20,000,000 g/mol.
2. The process according to claim 1 wherein the chelating agent and
the polymer are introduced as a mixture or the chelating agent and
the polymer are introduced separately.
3. The process according to claim 1 wherein the fibre material is a
cellulosic fibre material comprising a chemical, mechanical or
chemi-mechanical pulp or a recycled fibre material.
4. The process according to claim 1 wherein the treatment comprises
bleaching the fibre material with an alkaline peroxide solution in
the presence of the chelating agent and the polymer.
5. The process according to claim 4 wherein the bleaching is
preceded by a treatment with a chelating agent.
6. The process according to claim 1, wherein the treatment
comprises pretreating the fibre material in the aqueous medium
comprising the chelating agent and the polymer.
7. The process according to claim 6 wherein the pH of the aqueous
medium in the pretreatment is between 3 and 7.
8. The process according to claim 6 wherein the pretreatment is
followed by a bleaching with a peroxygen compound optionally in the
presence of the chelating agent and the polymer.
9. The process according to claim 8 wherein the peroxygen compound
is hydrogen peroxide, peracetic acid or Caro's acid.
10. The process according to claim 1 wherein the fibre material
comprises a recycled fibre material, and wherein the treatment
further comprises de-inking the recycled fiber material in the
aqueous medium comprising the chelating agent and the polymer.
11. The process according to any of claims 1 wherein in formula I n
is 0.4 to 0.9, m is 0.1 to 0.5, and k is 0 to 0.5.
12. The process according to claim 1 wherein the weight average
molecular weight of the copolymer is between 1,000 and 1,000,000
g/mol.
13. The process according to claim 1 wherein the total amount of
the chelating agent and the polymer in the treatment is 0.05 to 10
kg per ton of dry fibre material.
14. The process according to claims 1 wherein the weight ratio of
the polymer to the chelating agent is from 1:4 to 4:1, preferably
from 1:3 to 3:1.
15. The process according to claim 1 wherein the polymer is a
copolymer of 3-allyloxy-2-hydroxypropanesulfonic acid and at least
one of acrylic acid, methacrylic acid, maleic acid, itaconic acid,
or a salt thereof.
16. The process according to claim 1 wherein the chelating agent is
a compound having the following general formula ##STR14## wherein p
is 0 or an integer of 1 to 10, R.sub.3, R.sub.4, R.sub.5, R.sub.6
and R.sub.7 are independently a hydrogen atom or an alkyl chain
having 1 to 6 carbon atoms and containing an active chelating
ligand.
17. The process according to claim 1 wherein the chelating agent is
a compound having the following general formula ##STR15## wherein q
is an integer of 3 to 10, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are
independently a hydrogen atom or an alkyl chain having 1 to 6
carbon atoms and containing an active chelating ligand.
18. The process according to claim 1 wherein the chelating agent is
a compound having the following general formula ##STR16## wherein
R.sub.8 is a hydrogen atom, an alkyl group containing 1 to 6 carbon
atoms or an alkyl chain having 1 to 6 carbon atoms and containing a
carboxylic, phosphonic or hydroxyl group, R.sub.9 is a hydrogen
atom, hydroxyl group, phosphonic group, carboxylic group or alkyl
chain having 1 to 6 carbon atoms and containing one or two
carboxylic groups, and R.sub.10 is a hydrogen atom, hydroxyl group,
carboxylic group, alkyl group containing 1 to 6 carbon atoms or
alkyl chain having 1 to 6 carbon atoms and containing a carboxylic
group, or a salt thereof.
19. A composition comprising a chelating agent and a polymer having
the following general formula ##STR17## wherein R.sub.1 is a
hydrogen atom or an alkyl group containing 1 to 12 carbon atoms,
R.sub.2 is --COOM or --CH.sub.2COOM, M is a hydrogen atom, an
alkali metal ion, an alkaline earth metal ion, an ammonium ion or a
mixture thereof, n, m and k are molar ratios of corresponding
monomers, wherein n is 0 to 0.95, m is 0.05 to 0.9, and k is 0 to
0.8, and (n+m+k) equals 1, and the weight average molecular weight
is between 500 and 20,000,000 g/mol.
20. The composition according to claim 19 wherein in formula I n is
0.4 to 0.9, m is 0.1 to 0.5, and k is 0 to 0.5.
21. The composition according to claim 19 wherein the weight
average molecular weight of the copolymer is between 1,000 and
1,000,000 g/mol and preferably between 2,000 g/mol and 500,000
g/mol.
22. The composition according to claim 19 wherein the weight ratio
of the polymer to the chelating agent is from 1:4 to 4:1,
preferably from 1:3 to 3:1.
23. The composition according to claim 19 wherein the polymer is a
copolymer of 3-allyloxy-2-hydroxypropanesulfonic acid and at least
one of acrylic acid, methacrylic acid, maleic acid, itaconic acid
or a salt thereof.
24. The composition according to claim 19, wherein the chelating
agent is a compound having the following general formula ##STR18##
wherein p is 0 or an integer of 1 to 10, R.sub.3, R.sub.4, R.sub.5,
R.sub.6 and R.sub.7 are independently a hydrogen atom or an alkyl
chain having 1 to 6 carbon atoms and containing an active chelating
ligand.
25. The process of claim 1, wherein treatment of the fibre material
further comprises bleaching the fibre material in an aqueous
medium.
26. The process of claim 1, wherein treatment of the fibre material
further comprises deinking of a recycled fibre material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the treatment
of a fibre material, especially a cellulosic fibre material in the
presence of a chelating agent and a polymer, and to a composition
comprising a chelating agent and a polymer. The composition can be
used as a pretreatment in the bleaching with an peroxygen compound
of chemical, mechanical, chemi-mechanical and de-inked pulps and in
deinking of recycled fibers and in alkaline peroxide bleaching of
mechanical, chemical, chemi-mechanical and de-inked pulps. The
composition can also be used in deinking of recycled fibers. The
composition replaces partly or totally silicate as a stabilizer,
especially in the treatment of mechanical and deinked pulps. The
present invention also relates to a process for bleaching a
cellulosic fibre material with a peroxide compound in an aqueous
alkaline medium by using said composition.
DESCRIPTION OF THE RELATED ART
[0002] It is well-known that chelating agents can be used as
pretreatment for removing harmful metal ions, i.e. generally such
transition metal ions as iron and manganese before pulp is bleached
with a peroxygen compound, such as hydrogen peroxide, peracetic
acid or Caro's acid. In alkaline peroxide bleaching of mechanical
pulps, in bleaching of de-inked pulp (DIP) made from recovered
waste paper and in the deinking of recovered waste paper, water
glass (alkali silicate) and a chelating agent can be added.
[0003] Since the common chelating agents such as
polyaminopolycarboxylates, e.g. EDTA and DTPA and the corresponding
methylenephosphonic acid derivatives of the polyamines are
non-biodegradable or show a low biodegradation, there is a target
to decrease the use of the common chelating agents as pretreatment
agents.
[0004] Alkaline silicate solutions normally called water glass have
been used in stabilizing hydrogen peroxide solutions, which are
used in alkaline peroxide bleaching of mechanical pulps.
[0005] Water glass is used alone or together with peroxide in
de-inking of recovered papers. Sometimes the de-inked pulp is also
bleached with alkaline peroxide.
[0006] The use of water glass in alkaline peroxide bleaching of
chemical pulps has been published, but the method cannot be
utilized in full scale, since the silicate can cause very severe
precipitation problems. Another disadvantage with water glass is
that when the bleaching liquors are recycled and ultimately fed
into the recovery boiler, where the so-called black liquor from the
cooking process after concentration is burned, the silicate will
cause severe scaling and thus decrease the heat transfer in the
recovery boiler, which in worst case can cause an explosion of the
recovery boiler. Further the use of the silicate can cause highly
dusting.
[0007] If the silicates, e.g. in form of the water carry-over, will
enter the paper making process, they will disturb the papermaking
process, e.g. by precipitating on hot surface, causing holes in the
paper reel etc.
[0008] It is known that hydrogen peroxide will decompose very
rapidly in an alkaline milieu in the presence of transition metal
ions. The most abundant of these ions in pulps are iron and
manganese. The copper ion is also very detrimental for alkaline
hydrogen peroxide, but normally it can enter the process only via
used process waters.
[0009] It is also known that iron will start to precipitate already
below pH 7, first in colloidal form. The formed iron hydroxides,
oxyhydroxides etc are much more catalytically active than iron
ions. Also manganese can, at least partly, be in precipitated form,
but it has been shown that in the presence of hydrogen peroxide,
manganese should be in dissolved form.
[0010] The theory of the function of water glass varies, but one
theory is that water glass will deactivate the catalytic surface of
iron and other heavy metal ion "precipitates". In order to avoid
the detrimental effect of manganese ions, a chelating agent is
often introduced into the bleaching process or the pulp is
pretreated with a chelating agent. The most common chelating agents
are EDTA and DTPA, which belong to the group of
polyaminopolycarboxylates. The corresponding phosphonates, EDTMPA
and DTPMPA can also be used, but they are much more expensive than
the polyaminopolycarboxylates. They have also the disadvantage that
they contain phosphorus, which is not a wanted component, when the
environmental regulations are becoming stricter and stricter.
[0011] In the deinking of waste paper, water glass has also other
functions, e.g. water glass improves ink detachment, it will
disperse the ink and act as a buffer keeping the pH constant.
Therefore a partly replacement of water glass would also be
advantageous and at the same time decrease the precipitation
problems connected with the use of water glass.
[0012] According to the above there is a need to partly or totally
replace water glass (silicates) in alkaline peroxide bleaching
processes and in pulping processes, which use water glass, e.g. in
alkaline peroxide bleaching of mechanical and de-inked pulps and in
de-inking of recovered paper. There have been suggestions to use
phosphonates, but they should be used in quite high dosages and the
phosphorus problem in the waste waters would still remain. Since
the common phosphonates are non-biodegradable, there has been much
studies about they adverse effect on mobilizing heavy metals, e.g.
from sediments in waterways. If phosphonates would be used, the
dosage of these substances should be decreased.
[0013] A pretreatment method for bleaching pulp with hydrogen
peroxide in alkaline conditions in the presence of sodium silicate
and adding 0.05-1% by weight (based on dry pulp) of a copolymer of
3-allyloxy-2-hydroxypropanesulfonic acid (AHPS) and (meth)acrylic
acid in the pretreatment is described in the Japanese patent
publication JP 1266295 (published 24 Oct. 1989).
[0014] According to the Japanese patent application JP 1148890
(published 12 Jun. 1989) the same kind of polymer in an amount of
0.05-1% by weight (based on dry pulp) has been used instead of e.g.
DTPA in alkaline peroxide bleaching. In JP 1148890 the bleaching
performance of a number of different AHPS-acrylic acid copolymers
are shown and compared e.g. with the performance of DTPA.
[0015] In the both JP patent applications the tested amounts are
very big, since normally the chelating agents are used in an amount
of 0.5 to 2 kg per ton pulp as 100% sodium salt.
[0016] There are also patents covering the use of
poly-alfa-hydroxyacrylic acid (PHAA) instead of water glass, but
PHAA is very expensive to produce.
SUMMARY OF THE PRESENT INVENTION
[0017] According to the present invention it has now surprisingly
been found that by using a copolymer of AHPS and an unsaturated
carboxylic acid, such as acrylic acid, methacrylic acid, maleic
acid or itaconic acid, together with a chelating agent, either
mixed together or added separately, a very good bleaching
performance can be achieved and a total replacement of water glass
can be achieved, if necessary from the pulping and paper making
point of view. Surprisingly, the combination of the copolymer and a
chelating agent can very effectively be used as a pretreatment
agent before a bleaching of a chemical, mechanical or de-inked pulp
with a peroxygen compound, such as hydrogen peroxide, peracetic
acid or Caro's acid. The present invention makes it possible to
partially or totally replace water glass in bleaching and deinking
processes by using the combination of the copolymer and a chelating
agent.
[0018] The present invention provides a process for treatment of a
fibre material comprising the step of contacting the fibre material
in an aqueous medium with a chelating agent and the above
copolymer. The copolymer and the chelating agent can be added
separately or preferably as a ready made mixture (composition).
[0019] The present invention also relates to a composition
comprising the copolymer and the chelating agent.
[0020] The composition and process according to the invention can
be used as a pretreatment of all kind of pulps, chemical pulps,
mechanical, chemi-mechanical pulps and deinked pulps, which are
bleached with alkaline peroxide.
[0021] The composition and process according to the invention can
also be used in the bleaching of all kind pulps, chemical pulps,
mechanical, chemi-mechanical pulps and deinked pulps, which use
hydrogen peroxide as the bleaching agent.
[0022] The composition and process are also suitable in deinking of
recycled pulps, in which water glass and hydrogen peroxide are
commonly used.
[0023] The composition can also be used in sodium dithionite
bleaching of mechanical and de-inked pulps.
[0024] The alkaline peroxide bleaching process for mechanical,
chemi-mechanical and de-inked pulps according to the invention can
be practiced as a single stage of bleaching or in a two-stage
process, where the pre-bleached pulp is entering the second stage.
Any consistency can be used, but it is most preferable to use
medium consistency in the first stage and high consistency in the
second stage.
[0025] If needed, the bleaching can be preceded by a pretreatment
with a chelating agent or preceded by a pretreatment according to
the invention in order to reduce the amount of transition metals
entering the bleaching process.
[0026] In de-inking process the polymer composition can be used in
repulping or disperger or in a separate bleaching stage or any
process stage where hydrogen peroxide is present.
[0027] The composition, either as ready made mixture or as
combination of the polymer and chelating agent, can be used as
total or partial replacement in those processes, where water glass
are commonly used.
[0028] The effect of the combination of a chelating agent and the
polymer according to the invention in pretreatment may depend on
that the common chelating agents, polyaminopolycarboxylates, such
as EDTA and DTPA, and polyaminopolymethylenephosphonic acid
derivatives, such as EDTMPA and DTPMPA, very strongly chelate
transition metal ions such as e.g. iron and manganese ions. The
polymers used according to the invention bind very strongly
alkaline earth metal ions, especially calcium ions. When the
concentration of the alkaline earth metal ions is in very big
excess in relation to the transition metal ions as it is often in
case when e.g. white water from papermaking process is recycled to
the pulping and bleaching operation, the chelating agents are also
consumed for binding the alkaline earth metal ions. By addition a
very strong calcium binder the amount of a conventional chelating
agent can be reduced. Thus also the amount of nitrogen discharged
in effluent water will be decreased, which is advantageous for the
protection of the environment.
[0029] The theory how the polymer and chelating agent will work
together is not clear, since the polymer itself cannot stabilize
very well alkaline hydrogen peroxide solution and also gives in
general poor bleaching performance. The chelating agents stabilize
quite well the above mentioned alkaline peroxide, but cannot give a
good bleaching result. The common chelating agents mentioned above,
will bind the soluble manganese ions in the alkaline peroxide
solutions, but since iron is then in solid form, either colloidal
or in precipitated form, chelating agents cannot any more bind the
solid compounds. The same is valid for the solid forms of manganese
compounds. The polymer somehow binds to the solid surfaces or
inactivates the catalytic effect of the solid particles. Thus a
combined effect will be obtained. The common chelating agents
cannot, when used alone, give a good bleaching performance, i.e.
for chemical pulps, small viscosity loss and high brightness gain
and a sufficient amount of residual peroxide, and for mechanical
pulps and deinked pulps high brightness gain and a sufficient
amount of residual peroxide, which indicates that peroxide has
mainly been consumed for bleaching and not for decomposition
processes. Therefore there must be some synergetic effect between
the polymers and the common chelating agents used according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] In a first aspect of the present invention there is provided
a process for the treatment of a fibre material comprising the step
of contacting the fibre material in an aqueous medium with a
chelating agent and a polymer having following general formula
##STR2##
[0031] wherein
[0032] R.sub.1 is a hydrogen atom or an alkyl group containing 1 to
12 carbon atoms,
[0033] R.sub.2 is --COOM or --CH.sub.2COOM,
[0034] M is a hydrogen atom, an alkali metal ion, an alkaline earth
metal ion, an ammonium ion or a mixture thereof,
[0035] n, m and k are molar ratios of corresponding monomers,
wherein n is 0 to 0.95, m is 0.05 to 0.9, and k is 0 to 0.8, and
(n+m+k) equals 1, and
[0036] the weight average molecular weight is between 500 and
20,000,000 g/mol.
[0037] In a second aspect of the present invention there is
provided a composition comprising a chelating agent and a polymer
having following formula ##STR3##
[0038] wherein
[0039] R.sub.1 is a hydrogen atom or an alkyl group containing 1 to
12 carbon atoms,
[0040] R.sub.2 is --COOM or --CH.sub.2COOM,
[0041] M is a hydrogen atom, an alkali metal ion, an alkaline earth
metal ion, an ammonium ion or a mixture thereof,
[0042] n, m and k are molar ratios of corresponding monomers,
wherein n is 0 to 0.95, m is 0.05 to 0.9, and k is 0 to 0.8, and
(n+m+k) equals 1, and
[0043] the weight average molecular weight is between 500 and
20,000,000 g/mol.
[0044] The composition of the present invention can be used as a
stabilizer in the bleaching of a fibre material in an aqueous
medium or as a stabilizer in the deinking of a recycled fibre
material.
[0045] The above alkali metal ion is preferably sodium or potassium
ion, and the alkaline earth metal ion is preferably magnesium
ion.
[0046] A preferred comonomer with AHPS is acrylic acid
(R.sub.1.dbd.H), methacrylic acid (R.sub.1.dbd.CH.sub.3), maleic
acid (R.sub.2.dbd.COOM) or itaconic acid
(R.sub.2.dbd.CH.sub.2COOM). When k is 0 in formula I the preferred
comonomer is acrylic acid or methacrylic acid, and when n is 0 the
preferred comonomer is maleic acid or itaconic acid. When both k
and n are not 0 the preferred comonomers with AHPS are
(meth)acrylic acid and maleic acid or itaconic acid.
[0047] The monomers are randomly distributed along the polymer
chain of formula I, and preferably n is 0.4 to 0.9, m is 0.1 to
0.5, and k is 0 to 0.5.
[0048] If the system in pretreatment or in alkaline peroxide
bleaching contains high amount of calcium ions, as is the case,
when so-called white water from papermaking process is circulated
to the pulping and/or bleaching operations, it is advantageous to
use maleic acid or itaconic acid (k>0) as one of the comonomers
in order to increase the calcium binding ability of the polymer. It
is preferable in normal cases that the polymer according to the
invention only contains AHPS and a monomer containing one
carboxylic acid, such as acrylic acid, since a copolymer comprising
multiple monomers is usually more difficult to produce.
[0049] The weight average molecular weight of the copolymer of
formula I should be between 500 and 20,000,000 g/mol, preferably
between 1,000 and 1,000,000 g/mol and most preferably between 2,000
g/mol and 500,000 g/mol.
[0050] If the weight average molecular weight is lower than about
500 g/mol, the efficiency of the polymer becomes too low. If the
average molecular weight is higher than 20,000,000 g/mol, handling
and dosage become a problem due to high viscosity of the polymer
solution.
[0051] To increase the molecular weight of the copolymer and/or to
enhance the efficiency of the copolymer, a cross linker may be used
in an amount of 0 to 20% by mole, preferably 0 to 10% by mole, of
the total monomer content. Suitable cross linkers are, for example
methylenebisacrylamide, ethylene glycol divinyl ether, di(ethylene
glycol)divinyl ether, tri(ethylene glycol)divinyl ether and vinyl
or allyl terminated polymers, but are not limited to these.
[0052] To decrease molecular weight of the copolymer and/or to
enhance the efficiency of the copolymer, a chain transfer agent may
be used in an amount of 0 to 20% by mole, preferably 0 to 10% by
mole, of the total monomer content. Suitable chain transfer agents
are, for example thiols (e.g. butylmercaptan) and alcohols (e.g.
isopropanol), but are not limited to these.
[0053] The chelating agent to be used together with the copolymer
of formula I may be a chelating having formula II, III or IV
below.
[0054] A preferred chelating agent is a compound having following
general formula ##STR4##
[0055] wherein
[0056] p is 0 or an integer of 1 to 10,
[0057] R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are
independently a hydrogen atom or an alkyl chain having 1 to 6
carbon atoms and containing an active chelating ligand, such as a
carboxylic, phosphonic or hydroxyl group or a salt thereof.
[0058] The alkyl chain is preferably methylene --CH.sub.2-- or
ethylene --CH.sub.2CH.sub.2--.
[0059] In formula II R.sub.3, R.sub.4, R.sub.6 and R.sub.7
preferably represent the same group.
[0060] Examples of chelating agents according to the above formula
II are polyaminopolycarboxylic acids and
polyaminopolymethylenephosphonic acids.
[0061] The polyaminopolycarboxylic acids can be produced by the
conventional route from the polyamine and formaldehyde and sodium
cyanide or hydrocyanic acid. The more suitable route for small
scale production is to use a haloacetic acid, especially
monochloroacetic acid as a reactant.
[0062] Preferred polyaminopolycarboxylic acids are:
[0063] DTPA: p=1,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.R.sub.7.dbd.--CH.sub.2COO-
H
[0064] TTHA: p=2,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.R.sub.7.dbd.--CH.sub.2COO-
H
[0065] EDTA: p=0,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.--CH.sub.2COOH
[0066] HEDTA: p=0,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.--CH.sub.2COOH,
R.sub.5.dbd.--CH.sub.2CH.sub.2OH
[0067] The polyaminopolymethylenephosphonic acids are made
conventionally from the corresponding polyamine, formaldehyde and
phosphonic acid. With the higher amines a full substitution with
acetic acid groups or methylenphosphonic acid groups will become
more and more difficult. These chelating agents will also perform
well in the composition but an incomplete substitution will make
the chelating agents more prone for decomposition by hydrogen
peroxide.
[0068] Preferred polyaminopolymethylenephosphonic acids are:
[0069] DTPMPA: p=1,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.R.sub.7.dbd.--CH.sub.2POO-
.sub.2H.sub.2
[0070] TTHMPA: p=2,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.R.sub.7.dbd.--CH.sub.2POO-
.sub.2H.sub.2
[0071] EDTMPA: p=0,
R.sub.3.dbd.R.sub.4.dbd.R.sub.5.dbd.R.sub.6.dbd.--CH.sub.2POO.sub.2H.sub.-
2
[0072] Another preferred chelating agent is a compound having
following general formula ##STR5##
[0073] wherein
[0074] q is an integer of 3 to 10,
[0075] R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently a
hydrogen atom or an alkyl chain having 1 to 6 carbon atoms and
containing an active chelating ligand, such as a carboxylic,
phosphonic or hydroxyl group or a salt thereof.
[0076] The alkyl chain is preferably methylene --CH.sub.2-- or
ethylene --CH.sub.2CH.sub.2--.
[0077] In formula III R.sub.3, R.sub.4 and R.sub.6 preferably
represent the same group.
[0078] Examples of chelating agents according to the above formula
III are the commercially available hexamethylenediamine
tetra(acetic acid) (q=6) and tetramethylenediamine
tetra(methylenephosphonic acid) (q=4) having following formulae.
##STR6##
[0079] Yet another preferred chelating agent is a compound having
following general formula ##STR7##
[0080] wherein
[0081] R.sub.8 is a hydrogen atom, an alkyl group containing 1 to 6
carbon atoms or an alkyl chain having 1 to 6 carbon atoms and
containing a carboxylic, phosphonic or hydroxyl group,
[0082] R.sub.9 is a hydrogen atom, hydroxyl group, phosphonic
group, carboxylic group or alkyl chain having 1 to 6 carbon atoms
and containing one or two carboxylic groups, and
[0083] R.sub.10 is a hydrogen atom, hydroxyl group, carboxylic
group, alkyl group containing 1 to 6 carbon atoms or alkyl chain
having 1 to 6 carbon atoms and containing a carboxylic group, or a
salt thereof.
[0084] The alkyl chain is preferably methylene --CH.sub.2-- or
ethylene --CH.sub.2CH.sub.2--.
[0085] An example of the non-nitrogen containing chelating agents
according to the above formula IV is
1-hydroxyethylidene-1,1-diphosphonic acid (HEDP).
[0086] Though the formulas of the chelating agents are depicted
above as acids, they are commercially normally sold as their alkali
salts, mainly as their sodium salts and the formulas given above
have to be understood as including both the free acids and their
salts.
[0087] The polymer and the chelating agent can be added separately
or as a composition mixture. The weight ratio of the polymer
(calculated as solids) to the chelating agent (calculated as 100%
chelating agent as sodium salt) is preferably from 1:4 to 4:1, more
preferably from 1:3 to 3:1.
[0088] The total amount of the polymer (as solids) and the
chelating agent (as 100% sodium salt) added separately or as a
mixture, is preferably 0.05-10 kg per ton of dry fibre material,
more preferably 0.1-5 kg per ton of dry fibre material, and most
preferably 0.2 to 4 kg per ton of dry fibre material.
[0089] The fibre material is preferably a cellulosic fibre
material, especially a chemical, mechanical, chemi-mechanical or
deinked pulp. The cellulosic fibre material can also be any
regenerated cellulose material, such as viscose, or flax or
cotton.
[0090] If a composition mixture is made according to the invention,
the normal content of active materials in the mixture can be at
least 10%, preferably at least 15%, and more preferably at least
20% by weight, but also more diluted solutions can be used in the
application process.
[0091] In one embodiment of the process of the present invention
the treatment comprises bleaching the fibre material with an
alkaline peroxide solution in the presence of the chelating agent
and the polymer.
[0092] The bleaching of chemical pulp can be carried out at
temperatures of from 50.degree. C. to 150.degree. C. and at all
practical consistencies. The residence time in the bleaching can
vary within a wide range, from 30 to 240 minutes, preferably from
45 to 180 minutes and most preferably from 60 to 120 minutes. The
residence time will also depend on the temperature used in the
bleaching.
[0093] The stages can also be reinforced with oxygen, the
abbreviation of stages depicted in the professional literature as
EOP, Eop, PO or OP.
[0094] The peroxide bleaching of mechanical pulps with the process
according to the invention can comprise all kind of mechanical
pulps, e.g. stone groundwood pulp (SGW), refiner mechanical pulp
(RMP), pressure groundwood (PGW), thermo-mechanical pulp (TMP), but
also chemically treated high-yield pulps such as
chemithermomechanical pulp (CTMP). The invention is also useful in
bleaching of deinked pulps. Deinked pulp can be made using mixed
office waste (MOW), newsprint (ONP), magazines (OMG) etc. as raw
material and the polymer mixture can be used in any process stage
where peroxide is used. The invention can also be practiced in
refiner bleaching of mechanical pulps and in alkaline peroxide
mechanical pulp (APMP), in which wood chips are impregnated with
alkaline peroxide solution before refining. In these applications
the invention is very advantageous, since the biggest obstacle to
use hydrogen peroxide in these applications has been that water
glass cannot be used, since they will e.g. fasten to the refiner
plates and thus making the process unpractical.
[0095] The residence time in the bleaching can vary within a wide
range, from 30 to 240 minutes, preferably from 45 to 180 minutes
and most preferably from 60 to 120 minutes. The residence time will
also depend on the temperature used in the bleaching.
[0096] The composition according to the invention can be used as a
mixture or the ingredients can be added separately.
[0097] The bleaching of mechanical pulps can be carried out at a
temperature of from 30.degree. C. to 90.degree. C., preferably at a
temperature of from 50.degree. C. to 90.degree. C. The bleaching
can be carried out at a consistency of choice, but it is most
preferably to carry out the bleaching at a high consistency, i.e.
about 30% or higher. Bleaching can also be carried in two stages
with a dewatering stage between the stages. The stages can be
carried out at a consistency of choice, but it is most preferably
to use medium consistency in the first stage and a high consistency
in the second stage. This makes it possible to remove the
detrimental substances efficiently.
[0098] The bleaching stage can be preceded by a chelating agent
stage or a pretreatment according to the invention, discussed in
more detail below, and dewatering and thus improve the bleaching
performance. In the chelating agent stage any of the above defined
chelating agents can be used.
[0099] The ratio between the alkali and hydrogen peroxide can vary
in a wide range, depending on raw materials and degree of
bleaching. Also alternative alkali sources, like sodium carbonate,
can be utilized. The use of sodium carbonate is especially
preferably to use, at least as a partial replacement of sodium
hydroxide, when wastepaper is deinked with the total replacement of
water glass using the composition according to the invention. The
necessary buffer capacity can be ensured in this way.
[0100] In another embodiment of the process of the present
invention the treatment comprises pretreating the fibre material in
the aqueous medium comprising the chelating agent and the
polymer.
[0101] The pretreatment according to the invention can be utilized
for all kind of chemical and mechanical pulps.
[0102] The pretreatment can be followed by a bleaching with a
peroxygen compound optionally in the presence of the chelating
agent and the polymer. The peroxygen compound can be hydrogen
peroxide, peracetic acid or Caro's acid.
[0103] The pretreatment of chemical pulps can also precede such
stages, in which another peroxygen chemical than hydrogen peroxide
is used, e.g. a peracetic acid, Caro's acid etc. stage. If the
stage is followed by an alkaline stage comprising the use of
hydrogen peroxide, the treatment can also carried out after the
above mentioned peroxygen stage. Depending on the raw material and
the process the treatment can also be carried out only after the
mentioned peroxygen stage.
[0104] The consistency of this pretreatment is preferably around
10% in order to ensure an efficient metal removal. The pH is
preferably from 3 to 7, more preferably from 4 to 6.5 and most
preferably from 4.5 to 6. The pretreatment can be carried at any
temperature, but it is preferably carried at the same temperature
as the bleaching stage, but however below 100.degree. C.
[0105] In yet another embodiment of the process of the present
invention the treatment comprises de-inking recycled fibre material
in the aqueous medium containing the chelating agent and the
polymer.
[0106] In the de-inking process the polymer composition according
to the invention can be used in repulping of wastepaper or in a
disperger or in a separate bleaching stage or any process stage
where hydrogen peroxide is present.
[0107] The pH in the alkaline bleaching, including the de-inking in
the presence of hydrogen peroxide, is from 7 to 13, preferably from
7 to 12, and more preferably from 7to 11.
[0108] The present invention is illustrated by following examples,
which will not limit the scope of the invention.
[0109] In this specification the percentages are % by weight unless
otherwise specified. In the tables below the amounts of chemicals
given as kg refer to kg per ton dry pulp.
EXAMPLE 1
Polymerization of AHPS and Acrylic Acid
[0110] Preparation of poly(acrylic
acid-co-3-allyloxy-2-hydroxypropanesulfonic acid, sodium salt)
aqueous solution; a 65:35 (mol) polymer
[0111] A four-necked glass reactor of 0.25 liters, equipped with a
heating/cooling jacket, an overhead stirrer, a thermometer, a
reflux condenser, a gas inlet and 2 reagent pumps, was charged with
3-allyloxy-2-hydroxypropanesulfonic acid, sodium salt 40% aqueous
solution (95.5 g). The solution was degassed with nitrogen and
temperature raised to 85.degree. C. While the solution was stirred,
there were pumped at constant rate acrylic acid 50% aqueous
solution (46.8 g) within 3 hours, and sodium persulfate 1.3%
aqueous solution (47.6 g) within 3 hours and 30 minutes. The
addition of the reagent solutions was started simultaneously. After
addition of the sodium persulfate solution the reaction mixture was
stirred for additional 1 hour and 30 minutes, while maintaining the
temperature at 85.degree. C. The reactor was cooled, and slightly
yellow and viscous aqueous copolymer solution was obtained.
[0112] A sample of the solution was treated with excess of
concentrated hydrochloric acid solution to convert the
corresponding sodium salts to free acids. Residual
3-allyloxy-2-hydroxypropanesulfonic acid content of the thus
obtained solution was determined by gas chromatography, and was
approximated to be 2.0% by weight. This refers to 90% conversion of
the 3-allyloxy-2-hydroxypropanesulfonic acid, sodium salt
monomer.
[0113] A sample of the first copolymer solution was neutralized
with sodium hydroxide to pH about 10. The molecular weight of the
thus obtained copolymer was determined by gel permeation
chromatography against poly(acrylic acid, sodium salt) standards.
Number and weight average molecular weights were approximated to be
9,000 g/mol and 48,000 g/mol, respectively.
[0114] In order to make a preliminary test about the suitability of
the stabilizers for alkaline peroxide solutions, stability tests
were carried out, i.e. following the decomposition of hydrogen
peroxide as a function of time. Since the results very nicely
followed the first order kinetics, the results are given as half
life time figures. If a very low half life time is obtained, e.g.
under some tens of minutes, the product is not suitable for
alkaline peroxide bleaching. If the half life time is more than 100
minutes, the product may be suitable in alkaline peroxide bleaching
without sodium silicate, but the result does not guarantee a good
bleaching performance. Since the transition metal ions, especially
in wood abundantly present iron and manganese, will decompose
alkaline hydrogen peroxide, the tests were carried out in the
presence of these ions.
EXAMPLE 2
Stability Test of Alkaline Peroxide Solution (Comparison with
DTPA)
[0115] A solution containing Fe and Mn (as sulphates, Fe(II) 2 ppm,
Mn(II) 2 ppm), polymer (PAHPS-AA prepared in Example 1) and DTPA
was prepared and pH adjusted to 10. The temperature was raised to
50.degree. C. The solution was stirred and hydrogen peroxide added
in to concentration of 3 g/l. The pH was readjusted to 10, and the
hydrogen peroxide concentration measured as a function of time
(determined by standard iodometric method). The measurement time
was 90 minutes. The half life time of the hydrogen peroxide was
thus calculated. TABLE-US-00001 Substance/Dosage/ Half life time
t1/2 Polymer (as solid) [ppm] -- 140 40 75 100 DTPA (as 97%) [ppm]
140 -- 100 65 40 t1/2 [min] 190 15 110 180 220
[0116] It can be found that the polymer itself has no stabilizing
effect on alkaline peroxide bleaching in the presence of iron and
manganese ions. The DTPA can stabilize the solution quite well.
Surprisingly, a combination of the polymer and DTPA stabilizes the
solution better than DTPA alone, though the polymer has no
stabilizing effect itself.
EXAMPLE 3
[0117] An industrial TMP (spruce, picea abies) pulp was bleached in
laboratory using different stabilizers. The detailed reaction
conditions and chemical dosages are presented in table below. The
pulp contained 6.2 ppm Fe, 16 ppm Mn, 696 ppm Ca, and 2 ppm Cu. The
polymerization of PAHPS-AA used in this test is described in
example 1. DTPA and DTPMPA used in this test were of commercial
grade containing the normal side products of the process.
TABLE-US-00002 pulp 02077 02077 02077 02077 02077 02077 02077 02077
test No. 1 4 5 6 7 8 9 10 T, C. 70 70 70 70 70 70 70 70 t, min 120
120 120 120 120 120 120 120 Cs, % 12 12 12 12 12 12 12 12 Initial
pH 10.1 10.2 10.2 10.1 10.3 10.5 10.2 10.4 H2O2, kg 30 30 30 30 30
30 30 30 NaOH: H2O2 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 NaOH, kg 21 21
21 21 21 21 21 21 Waterglass: H2O2 0.8 0 0 0 0 0 0 0 Waterglass, kg
24 0 0 0 0 0 0 0 PAHPS-AA, kg 0 2 4 4 4 0 4 0 DTPA, kg 0 2 4 1 0 0
0 4 DTPMPA, kg 0 0 0 0 1 1 0 0 Residual H2O2, kg 17.2 21.1 20.9
22.9 21.8 19.76 11.7 10.8 Brightness, % ISO 74.5 74.8 74.9 74 74.3
74 72.3 72.4
[0118] The results show that the stabilizer according to the
invention gives a bleaching result equal to waterglass. The
combination of DTPMPA and PAHPS-AA (test No. 7) and the combination
of DTPA and PAHPS-AA (test No.s 4, 5 and 6) give good results.
However, PAHPS-AA alone (test No.9) and DTPA alone (test No. 10)
give lower brightness with higher peroxide consumption.
EXAMPLE 4
Bleaching Test with Chemical Pulp
[0119] Industrial softwood kraft pulp was chelated and peroxide
bleached in laboratory. Detailed reaction conditions and the metals
content of the pulp are presented in table below. TABLE-US-00003
pulp ref. 01185 01185 01185 01185 01185 No: 210 220 224 226 229
test Unbleached Q Q Q Q Q Q t,min 30 30 30 30 30 T,C 70 70 70 70 70
Cs, % 10 10 10 10 10 Initial pH 5.5 5.5 5.5 5.5 5.5 Final pH 5.8
5.8 5.7 5.7 5.7 DTPA, kg 0 2.5 0 0.5 2.5 PAHPS-AA, kg 0 0 2.5 0 2.5
Fe, ppm 17.9 7.3 14.8 10.1 7.0 8.2 Mn, ppm 40.9 29.6 2.3 24.8 5.3
3.8 Ca, ppm 1662 1006 920 1002 873 832 ##STR8## ##STR9## ##STR10##
##STR11## ##STR12## P P P P P P t,min 120 120 120 120 120 120 T,C
90 90 90 90 90 90 Cs, % 12 12 12 12 12 12 Initial pH 10.4 10.4 10.4
10.4 10.4 110.4 Final pH 9.9 9.8 9.7 9.6 10.0 10.1 NaOH, kg 6 6 6 6
6 6 H2O2, kg 15 15 15 15 15 15 PAHPS-AA, kg 0 0 0 0 2 0 DTPA, kg 0
0 0 0 2 0 Residual H2O2, kg 0.0 9.2 0.0 6.9 9.2 11.4 Residual NaOH,
kg 1.1 4.1 0.7 0.8 2.1 2.4 Brightness, % ISO 58.9 71.2 62.0 71.4
72.1 70.2 Kappa number 5.7 5.1 5.2 4.8 5.1 4.7 Viscosity, dm3/kg
811 849 796 827 872 892
[0120] The results show that PAHPS-AA polymer as such has no
significant chelating efficiency. However, the use of stabilizer
according to the invention as pre-treatment gives quite satisfying
result. Best result was obtained when the stabilizers were added in
peroxide bleaching stage.
EXAMPLE 5
[0121] An industrial TMP (spruce, picea abies) pulp was bleached in
laboratory using waterglass and/or stabilizer according to the
invention. The detailed reaction conditions and chemical dosages
are presented in table below. The pulp contained 6.2 ppm Fe, 16 ppm
Mn, 696 ppm Ca, and 2 ppm Cu. The polymerization of PAHPS-AA used
in this test is described in example 1. DTPA used in this test was
commercial grade containing the normal side products of the
process. TABLE-US-00004 No. 1 2 3 4 T, C. 70 70 70 70 t, min 120
120 120 120 Cs, % 12 12 12 12 Initial pH 10.1 10.1 9.8 10.2 Final
pH 8.1 7.9 7.9 7.9 H2O2, kg 30 30 30 30 NaOH: H2O2 0.7 0.7 0.7 0.7
NaOH, kg 21 21 21 21 Waterglass: H2O2 0.8 0.4 0.2 0 Waterglass, kg
24 12 6 0 PAHPS-AA, kg 0 2 2 2 DTPA, kg 0 2 2 2 Residual H2O2, kg
17.2 18.2 20.7 21.1 Brightness, % ISO 74.5 73.9 74.4 74.8
[0122] The results show that partial or total replacement of
waterglass gives as good bleaching results as waterglass alone.
EXAMPLE 6
[0123] The TMP sample used in previous examples 3 and 5 was
pretreated with stabilizer according to the invention and bleached
using the same stabilizer. Normal chelation using DTPA was as
reference. The results are shown in table below. TABLE-US-00005 Q Q
Trial no. 211 213 T,C 60 60 t,min 15 15 Cs,% 5 5 Initial pH 5.5 5.5
Final pH 5.6 5.5 PAHPS-AA, kg 0 2 DTPA, kg 2 2 P P Trial no. 212
214 t,C 70 70 t,min 120 120 Cs,% 12 12 Initial pH 10 10.1 H2O2, kg
30 30 NaOH:H2O2 0.7 0.7 NaOH, kg 21 21 Waterglass, kg 24 0
PAHPS-AA, kg 0 2 DTPA, kg 0 2 Residual H2O2, kg 19.7 21.2
Brightness, %ISO 74.1 74.8
[0124] The results show that pre-treatment with the stabilizer
according to the invention and bleaching using the same stabilizer
gives better bleaching results as compared to conventional DTPA
treatment.
EXAMPLE 7
[0125] An industrial TMP pulp was bleached in laboratory using
waterglass and/or stabilizer according to the invention with
different polymer:aminopolycarboxylate ratios. The results are
shown in table below. The pulp contained 4 ppm Mn and 5 ppm Fe. The
bleaching conditions were: temperature 70.degree. C., bleaching
time 120 min, Cs 12%, H.sub.2O.sub.2 30 kg/ton dry pulp and NaOH 30
kg/ton dry pulp. TABLE-US-00006 Experiment No. 1 2 3 4 5 6 7 8
Initial pH 10.8 10.7 11.0 10.9 10.9 10.8 10.9 10.9 Final pH 9.7 9.8
9.9 9.9 10 9.8 9.8 9.1 Sodium silicate, kg -- 24 -- -- -- -- -- --
polymer (as solid), kg -- -- 4 3 2 1 -- 1 DTPA (as 90%), kg -- --
-- 1 2 3 4 1 Residual H.sub.2O.sub.2, kg 3.0 11.2 4.9 8.2 11.8 8.7
6.2 12.5 Brightness, ISO % 72.6 77.1 74.7 76.2 77.4 76.1 74.2
76.9
[0126] The results show that the combination of polymer and
chelating agent gives better result than either of them alone.
EXAMPLE 8
[0127] Bleaching of DIP
[0128] An industrial sample of de-inked mixed office waste was
bleached in laboratory using waterglass and/or stabilizer according
to the invention. The detailed reaction conditions and results are
shown in table below. TABLE-US-00007 Time, min 80 80 80 80
Temperature, C. 73 73 73 73 Consistency, % 26 26 26 26 H2O2, kg/tp
12 12 12 12 NaOH, kg/tp 3.5 3.5 3.5 3.5 Waterglass, kg/tp 8 0 0 0
PAHPS-AA 0 0 2 1 DTPA, kg 0 0 2 2 Residual H2O2, kg/tp 6.6 0.1 7.8
2.8 Brightness, % ISO 85.1 90.4 87.4 90.7 89 According to No No Yes
Yes the invention?
[0129] The results show the beneficial effect of bleaching
stabilizer. The bleaching result was about the same with waterglass
and stabilizer according to the invention, while bleaching without
stabilizer consumes almost all peroxide and brightness is also
lower.
* * * * *